Polyimide Cover Substrate Hardness Flexibility Trade-off
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Solution Overview
Problem
Conventional flexible display substrates face issues with surface cracking and impact resistance due to the use of organic cured films, which compromise flexural properties and chemical resistance.
Innovation Solution
A polyimide cover substrate is developed with a urethane acrylate compound as a device protection layer on a polyimide film, optionally combined with silicon oxide, hard coating, and transparent electrode layers, enhancing flexural properties and impact resistance while maintaining optical transparency and chemical resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If an acryl- or epoxy-based organic cured film is formed on the surface of a transparent film to enhance hardness, then surface hardness is improved, but the film becomes inflexible and causes surface cracking problems in flexural properties or impact resistance
Solution Approach 1:
The patent changes the chemical composition parameters of the protective film from conventional acryl or epoxy resins to polyurethane acrylate resin, which has different molecular structure characteristics. This parameter change enables the film to achieve both hardness and flexibility, resolving the contradiction between surface hardness and flexural properties by selecting a resin with appropriate molecular weight (1,000-50,000 g/mol) and functional groups that provide both protective and flexible characteristics
Solution Approach 2:
The patent creates a composite structure by forming a protective film that combines polyurethane acrylate resin with specific functional groups on the transparent film surface. This composite approach integrates the hardness-providing acrylate groups with the flexibility-providing polyurethane backbone, achieving a material that simultaneously delivers surface protection and maintains flexural reliability
2Strength
If a hard-coat layer is formed on an upper side of an organic layer to achieve high hardness, then surface hardness is improved, but the overall structure becomes less flexible and more prone to cracking
Solution Approach 1:
The patent modifies the chemical parameters of the hard-coat layer by using polyurethane acrylate resin instead of conventional acryl or epoxy resins. This parameter change maintains the hardness function through acrylate groups while the polyurethane structure provides enhanced chemical resistance and flexibility, simultaneously improving hardness, chemical resistance, and reducing cracking susceptibility
Solution Approach 2:
The polyurethane acrylate resin acts as an intermediary material between the transparent film and the external environment. It provides a protective interface that delivers hardness for scratch resistance while its molecular structure serves as a mediator that maintains flexibility and chemical resistance, preventing the transmission of stress that would cause cracking in the underlying film
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a flexible substrate with improved flexural properties, impact resistance, solvent resistance, optical properties, and scratch resistance, suitable for use in flexible electronic devices.
Implementation Method 1
a device protection layer formed of a urethane acrylate compound on at least one side of the polyimide film
Data Source
Figure 1~6
Figure 7
AI summary
Disclosed is a polyimide cover substrate, which is configured such that a device protection layer is formed of a urethane acrylate compound on at least one side of a polyimide film, thereby exhibiting not only high flexural properties and impact resistance but also superior solvent resistance, optical properties and scratch resistance and low water vapor transmission rate, and thus can be effectively utilized as a cover substrate for a flexible electronic device.